You don't want to be mistaken, do you? Then, list the qualities that you look for in an individual who you want to date. It won't be amiss to say a few words about what your ideal match should not be. There more adamant qualities you write about, the more you ward off the undesirable.
For example, state that you won't date a heavy smoker or someone who has children. The person has been informed beforehand, he can't claim he did not read your ad. Saying at once what you are expecting from your future ideal match helps eliminating errors.
But be careful! There is no one totally defect free! Do not be too strict. Think of yourself first. Are you that perfect, you could demand your ideal match has no drawbacks at all? Also avoid pressure. Are you seeking someone ultra ordinary? The way some personal ads are compiled makes you think you should step into a certain role and be someone you are expected to be. You may try to play the role of course, but time goes on and you can't always be the right person, otherwise there is a good opportunity to loose your personality. You do need a particular soul near you, not a walking-talking doll. Otherwise, why bother yourself and other people on the internet, just go to the toy section of a department store.
Yes, and the last thing. What about your religion? If it is a matter of importance for you, then state that it is. A religious dispute is not the thing you are dreaming of. So better do not bother people who are only seeking someone, who is part of their faith.